let arr1 = ["A1", "A2", "B1", "B2", "C1", "C2"]
let arr2 = ["A", "B", "C"];
// res=['A1', 'A2', 'A', 'B1', 'B2', 'B', 'C1', 'C2', 'C']


function mergeArr(arr1,arr2) {
    // concat 用于连接两个数组 Set用于去重 解构为数组
    return [...new Set(arr1.concat(arr2))]
}

console.log(mergeArr(arr1, arr2));
